1. Field of the Invention
This invention relates to automatic power transmisions providing a plurality of gear reduction ratios, such as automatic mechanical transmissions (i.e. "AMTs"), and, to control systems and methods therefor. In particular, the present invention relates to control systems and methods for automatic mechanical transmission systems wherein gear selection and shift decisions are made and/or executed based upon measured and/or calculated parameters such as vehicle or transmission output shaft speed, transmission input shaft speed, engine speed, throttle position, rate of change of throttle position, rate of change of vehicle and/or engine speed and the like. More particularly, the present invention relates to a method for controlling an AMT system utilizing sensors for providing input signals indicative of throttle position, throttle position equal to or greater than at least a first minimum reference value ("idle") and throttle position equal to or greater than at least a second detented reference value ("kick-down"), including sensing of a faulty signal from one of such sensors, identifying the fault and modifying the system operation logic in tolerance of such identified fault.
2. Description of the Prior Art
The use of automatic transmissions of both the automatic mechanical type utilizing positive clutches and of the planetary gear type utilizing frictional clutches is well known in the prior art as are control systems therefor. Electronic control systems utilizing discrete logic circuits and/or software controlled microprocessors for automatic transmissions wherein gear selection and shift decisions are made based upon certain measured and/or calculated parameters such as vehicle speed (or transmission output shaft speed), transmission input shaft speed, engine speed, rate of change of vehicle speed, rate of change of engine speed, throttle position (usually expressed as a percentage of full throttle), rate of change of throttle position, full depression of the throttle (i.e. "kickdown"), at least minimal depression (foot-on) of throttle actuation of the braking mechanism, currently engaged gear ratio, and the like are known in the prior art. Examples of such automatic and semi-automatic transmission control systems for vehicles may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,648,290; 4,595,986; 4,576,263: 4,576,065: 4,569,255; 4,551,802: 4,527,447: 4,425,620; 4,463,427 4,081,065; 4,073,203; 4,253,348; 4,038,889; 4,226,295; 3,776,048, 4,208,929: 4,039,061: 3.974,720; 3,478,851 and 3,942,393, the disclosures of which are all hereby incorporated by reference.
While the above referenced automatic and semi-automatic transmission control systems, and similar systems, are effective to control an automatic transmission by selecting a desired gear ratio which will tend to optimize the fuel economy and/or performance of the vehicle in view of the sensed parameters/or commanding a shift into a selected gear ratio, such control systems were not totally acceptable as the predetermined programs utilized did not include self-diagnostic logic routines, or methods, to recognize and identify a fault in the input signals from one of the throttle position sensors and/or could not modify the predetermined program to provide a tolerance to such a sensed fault.